1. Technical Field
The present invention relates in general to downhole submersible pumps and, in particular, to an improved system, method, and apparatus for a downhole electrical submersible pump equipped with a fiber optic communications.
2. Description of the Related Art
Many different techniques have been used to monitor well bores during completion and production of well bores, reservoir conditions, estimating quantities of hydrocarbons, operating downhole devices in the well bores, and determining the physical condition of the well bore and downhole devices. Reservoir monitoring involves determining certain downhole parameters in producing well bores at various locations in one or more producing well bores in a field, typically over extended time periods.
Wire line tools are commonly used to obtain such measurements, which involves transporting the wire line tools to the well site, conveying the tools into the well bores, shutting down the production and making measurements over extended periods of time and processing the resultant data at the surface. Seismic methods wherein a plurality of sensors are placed on the earth's surface and a source placed at the surface or downhole are utilized to provide maps of subsurface structure. Such information is used to update prior seismic maps to monitor the reservoir or field conditions. Each of these methods is expensive. Moreover, the wire line methods occur at large time intervals and cannot provide continuous information about the well bore condition or that of the surrounding formations.
The use of permanent sensors in the well bore, such as temperature sensors, pressure sensors, accelerometers and hydrophones has been proposed to obtain continuous well bore and formation information. To obtain such measurements from the entire useful segments of each well bore, which may include multi-lateral well bores, requires using a large number of sensors. In turn, this requires a large amount of power, data acquisition equipment and relatively large space in the well bore, all of which may be impractical or prohibitively expensive.
Once the information has been obtained, it is desirable to manipulate downhole devices such as completion and production strings. Existing methods for performing such functions rely on the use of electrically operated devices with signals for their operation communicated through electrical cables. Because of the harsh operating conditions downhole, it is difficult for the electronics used in conventional downhole sensors to survive for any extended period of time.
For example, the MTBF of semiconductors is directly reduced by high temperatures. In addition, electrical cables are subject to degradation under these conditions. In addition, due to long electrical path lengths for downhole devices, cable reactance/resistance becomes significant unless large cables are used. This is difficult to do within the limited space available in production strings. In addition, due to the high reactance/resistance, power requirements also become large.
One type of configuration operates numerous downhole devices and is necessary in secondary recovery. Injection wells have been employed for many years in order to flush residual oil in a formation toward a production well and increase yield from the area. A common injection scenario is to pump steam down an injection well and into the formation which functions both to heat the oil in the formation and force its movement through the practice of steam flooding. In some cases, heating is not necessary as the residual oil is in a flowable form, however in some situations the oil is in such a viscous form that it requires heating in order to flow. Thus, by using steam one accomplishes both objectives of the injection well: to force residual oil toward the production well; and to heat any highly viscous oil deposits in order mobilize such oil to flow ahead of the flood front toward the production well.
One of the most common drawbacks of employing the method above noted with respect to injection wells is commonly identified as “breakthrough”. Breakthrough occurs when a portion of the flood front reaches the production well. As happens the flood water remaining in the reservoir will generally tend to travel the path of least resistance and will follow the breakthrough channel to the production well. At this point, movement of the viscous oil ends. Precisely when and where the breakthrough will occur depends upon water/oil mobility ratio, the lithology, the porosity and permeability of the formation as well as the depth thereof. Moreover, other geologic conditions such as faults and unconformities also affect the in-situ sweep efficiency.
While careful examination of the formation by skilled geologists can yield a reasonable understanding of the characteristics thereof and therefore deduce a plausible scenario of the way the flood front will move, it has not heretofore been known to monitor precisely the location of the flood front as a whole or as individual sections thereof. By so monitoring the flood front, it is possible to direct greater or lesser flow to different areas in the reservoir, as desired, by adjustment of the volume and location of both injection and production, hence controlling overall sweep efficiency. By careful control of the flood front, it can be maintained in a controlled, non fingered profile. By avoiding premature breakthrough the flooding operation is effective for more of the total formation volume, and thus efficiency in the production of oil is improved.
In production wells, chemicals are often injected downhole to treat the producing fluids. However, it can be difficult to monitor and control such chemical injection in real time. Similarly, chemicals are typically used at the surface to treat the produced hydrocarbons (i.e., to break down emulsions) and to inhibit corrosion. Likewise, it can be difficult to monitor and control such treatment in real time. In summary, there are many different ways of monitoring parameters in a well bore, however, an improved solution would be desirable.